Arsenic occurs naturally, and Michigan is one of a handful of states with unusually high arsenic concentrations in groundwater.
Arsenic was also used in insecticides for many years and it's still being used in some weed killers.
David Heath is a senior reporter at the Center for Public Integrity, and he investigated why a health assessment on arsenic from the U.S. Environmental Protection Agency has been delayed.
Why does this health assessment matter?
Heath said when the EPA first wants to determine how dangerous a toxic chemical is, they first do the science. These assessments can take a long time and the arsenic assessment has been going on for more than a decade.
"It's not until they have done the science to figure out exactly how dangerous a chemical is that they can really take action on it," Heath said. "So it really does come down to 'this is how they protect your health.'"
A single member of Congress, Rep. Mike Simpson, R-Idaho, was able to intentionally delay the EPA's health assessment for years.